Nanoparticle
Assembly

With the advances made in solution-phase materials chemistry
in the last 20 years, nanoparticles (NPs) can now be prepared
out of a wide spectrum of compositions with a high degree of
particle size and shape control. NPs are an intriguing class
of materials because their reduced physical dimensionality leads
to the appearance of catalytic, chemical, optoelectronic, and
magnetic properties not found in bulk materials. They remain
rather difficult to handle for applications, though, due to
their colloidal nature and their susceptibility to uncontrolled
aggregation. Thus, there is a need for synthetic methodologies
for creating functional materials out of NPs.

We recently discovered that, under specific solution conditions, cationic polyelectrolytes can induce
negatively-charged silica NPs to form micron-sized hollow spheres rather than the randomly structured
precipitate that would ordinarily result from flocculation. The polyelectrolyte (e.g., polyallylamine)
forms aggregates under the crosslinking action of a multivalent salt (e.g., EDTA). These aggregates act
as templates around which the NPs deposit to form a multilayer-thick NP/polymer shell. We term this form
of NP assembly as "polymer aggregate templating" and the resultant nanoparticle-assembled capsules as "NACs."